1. Field of the Invention
The invention relates to a safety system for use in an extremely unlikely case of an accident in a gas cooled high temperature reactor, more particularly, for use in a reactor housed with a plurality of steam generators in a prestressed concrete pressure vessel. equipped with absorber rod shutdown means and a reactor protection system for actuation of emergency shut-down systems and decay heat removal.
2. Description of the Related Technology
Nuclear reactors in general and gas cooled high temperature reactors in particular, are equipped with automatic regulating and control devices, in order to prevent or limit deviations from the planned operating behavior (operational control) and to place the plant automatically into a safe state if predetermined limiting values are exceeded. The latter is the purpose of the aforementioned reactor protection system actuating the emergency shut-down and an appropriate heat removal and aftercooling procedure.
All of the cases of disturbance to be considered in the licensing procedure with a probability of occurrence higher than about 10.sup. -5/ year are controlled by the reactor protection system, i.e., the effects on the environment remain within the limits determined by the radiation protection regulations. Accidents less likely than the above are not an object to be considered in the layout of the reactor and in the licensing procedure, however, certain precautionary measures to limit such accidents are required.
High temperature reactors already possess a high degree of safety in view of their location in a prestressed concrete pressure vessel and the properties specific to high temperature reactors, even in extremely unlikely accident situations, so that the extent of damage remains limited even in such cases. The extent of damage may be reduced even more by appropriate measures. DE-OS 32 12 322, expressly incorporated by reference herein, shows a process for the control of layout and hypothetical accidents in a high temperature reactor, wherein a plurality of successive steps are given, which are always initiated following the occurrence of a certain event (accident), automatically as a matter of principle (only if an intended measure is not initiated, are emergency measures carried out manually). The steps are designed so that each of them will prevent the failure of one of the four barriers present in a high temperature reactor for the retention of fission products.